Index: cfe/trunk/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaDeclAttr.cpp
+++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp
@@ -1898,7 +1898,16 @@
     }
   }
 
-  // FIXME: check if target symbol exists in current file
+  // Mark target used to prevent unneeded-internal-declaration warnings.
+  if (!S.LangOpts.CPlusPlus) {
+    // FIXME: demangle Str for C++, as the attribute refers to the mangled
+    // linkage name, not the pre-mangled identifier.
+    const DeclarationNameInfo target(&S.Context.Idents.get(Str), AL.getLoc());
+    LookupResult LR(S, target, Sema::LookupOrdinaryName);
+    if (S.LookupQualifiedName(LR, S.getCurLexicalContext()))
+      for (NamedDecl *ND : LR)
+        ND->markUsed(S.Context);
+  }
 
   D->addAttr(::new (S.Context) AliasAttr(AL.getRange(), S.Context, Str,
                                          AL.getAttributeSpellingListIndex()));
Index: cfe/trunk/test/Sema/alias-unused.c
===================================================================
--- cfe/trunk/test/Sema/alias-unused.c
+++ cfe/trunk/test/Sema/alias-unused.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -Wunneeded-internal-declaration -x c -verify %s
+// expected-no-diagnostics
+static int f() { return 42; }
+int g() __attribute__((alias("f")));
+
+static int foo [] = { 42, 0xDEAD };
+extern typeof(foo) bar __attribute__((unused, alias("foo")));